Micro electro mechanical device and manufacturing method thereof

ABSTRACT

To manufacture a micro structure and an electric circuit included in a micro electro mechanical device over the same insulating surface in the same step. In the micro electro mechanical device, an electric circuit including a transistor and a micro structure are integrated over a substrate having an insulating surface. The micro structure includes a structural layer having the same stacked-layer structure as a layered product of a gate insulating layer of the transistor and a semiconductor layer provided over the gate insulating layer. That is, the structural layer includes a layer formed of the same insulating film as the gate insulating layer and a layer formed of the same semiconductor film as the semiconductor layer of the transistor. Further, the micro structure is manufactured by using each of conductive layers used for a gate electrode, a source electrode, and a drain electrode of the transistor as a sacrificial layer.

BACKGROUND OF THE INVENTION

1. Field of the Present Invention

The present invention relates to a micro electro mechanical device (amicro electronic mechanical system) formed over an insulating substrate.In particular, the present invention relates to a micro mechanicalstructure of a micro electro mechanical device and a method formanufacturing the micro mechanical structure of the micro electromechanical device.

2. Description of the Related Art

In recent years, a micro mechanical system called MEMS has been activelyresearched. MEMS is abbreviation of Micro Electro Mechanical System andtranslated into a micro electro mechanical device, a micro electromechanical system, or the like. MEMS is also called a micro machine inJapan and is also called an MST (Micro System Technology) in Europe orthe like. In this specification, MEMS is also described as amicromachine or a micro electro mechanical device. MEMS corresponds toan electronic device in which a micro mechanical portion including “amovable micro structure having a three-dimensional structure” iscombined with “an electric circuit including a semiconductor element”which controls the mechanical portion. In addition, MEMS is also simplycalled a micro machine.

Since a MEMS can control its micro structure by an electric circuit, ithas been expected that an autonomous-distributed type system can beconstructed instead of a central-processing control type system such asa conventional device using a computer. For example, a MEMS can processdata obtained by a sensor by using an electric circuit and can drive anactuator or the like in accordance with data processing.

Many researches have been made on a micro machine. For example, anadvanced MEMS wafer level package has been proposed to solve a problemthat a manufacturing process cannot be used in facilities for wafermanufacturing and plastic assembly in Reference 1 (Japanese PublishedPatent Application No. 2001-144117). Reference 2 (Japanese PublishedPatent Application No. 2004-1201) discloses that preferable mechanicalcharacteristics are generated in a layer which forms a structure bycontrolling laser irradiation.

However, as disclosed in Reference 1, a micro structure which forms amicro machine is manufactured in a manufacturing process of asemiconductor element using a silicon wafer. In particular, in order toobtain a material having thickness and intensity enough formanufacturing of a micro structure, micro machines which are practicallyused are mainly manufactured by using silicon wafers. In addition,Reference 2 discloses only a cantilever which is a micro structure butdose not disclose integration of the micro structure with an electriccircuit at all.

SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a micro electromechanical device in which a micro structure and an electric circuitwhich controls the micro structure are integrated over the samesubstrate, and a manufacturing method thereof.

A micro electro mechanical device of the present invention includes amicro structure and an electric circuit which controls the microstructure over an insulating surface. The electric circuit iselectrically connected to the micro structure and includes a transistor.The micro structure at least includes a structural layer which is notfixed to a substrate and a structural layer part of which is fixed tothe substrate. Description “part of a structural layer is fixed to asubstrate” corresponds to that the structural layer has a portion whichis not fixed to the substrate. That is, the description “part of astructural layer is fixed to a substrate” corresponds to that part ofthe structural layer is fixed to the substrate so that a space is formedbetween the substrate and another part of the structural layer. At leastone of structural layers which form the micro structure is completelyseparated from the substrate and a movable range is limited by astructural layer fixed to another substrate. For example, the structurallayer which is completely separated from the substrate is used as arotor and a structural layer serving as a rotation axis of the rotor isformed so as to be fixed to the substrate, so that a movable range ofthe structural layer serving as the rotor is limited by the structurallayer serving as the rotation axis or the like.

In a micro electro mechanical device of the present invention, a microstructure includes a layer with a stacked structure which is the same asa stacked structure of a gate insulating layer and a semiconductor layerof a transistor as first and second structural layers. That is, themicro structure has structural layers including a layer which is formedof the same insulating film as the gate insulating layer and a layerwhich is formed of the same semiconductor film as the semiconductorlayer of the transistor.

As for a micro electro mechanical device in accordance with one aspectof the present invention, a semiconductor layer included in a microstructure has a multi-layer structure and crystalline structures oflayers are varied. Therefore, a defect of each layer is compensated sothat damage to the micro structure can be suppressed.

As for a micro electro mechanical device in accordance with anotheraspect of the present invention, a compound of a semiconductor with ametal like a silicide is included in a structural layer of a microstructure. Therefore, intensity of the structural layer can be improvedthan that of polycrystalline silicon and conductivity can also beimproved.

As for a method for manufacturing a micro electro mechanical device inaccordance with another aspect of the present invention, a layer formedof the same film as a gate electrode is used for a layer serving as asacrificial layer in order to provide a movable portion to a microstructure.

In a micro electro mechanical device of the present invention, a microstructure and an electric circuit which controls the micro structure areformed over the same insulating surface, so that mechanical intensity ofa connection portion of the electric circuit and the micro structure ishigh and poor connection is hardly generated. In addition, by a methodfor manufacturing the micro electro mechanical device of the presentinvention, a micro electro mechanical device can be provided in which amicro structure and an electric circuit which controls the microstructure are formed over the same insulating surface through the samestep. That is, there is no separation of steps such that the microstructure is manufactured after the electric circuit is manufactured orthe electric circuit is manufactured after the micro structure ismanufactured. Thus, the method for manufacturing is simplified so thatthe micro electro mechanical device can be manufactured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a structural example of a micro electromechanical device of the present invention; FIG. 1A is a cross-sectionalview of the micro electro mechanical device; and FIG. 1B is a top planview of the micro structure (Embodiment Mode 1);

FIGS. 2A to 2E are cross-sectional views showing a method formanufacturing a micro electro mechanical device of the present invention(Embodiment Mode 1);

FIGS. 3A and 3B are cross-sectional views showing a manufacturing methodof a micro electro mechanical device of the present invention(Embodiment Mode 1);

FIG. 4 is a top plan view of a micro structure which is in the middle ofmanufacturing and is a top plan view of a first conductive layer (afirst sacrificial layer) (Embodiment Mode 1);

FIG. 5 is a top plan view of a micro structure which is in the middle ofmanufacturing and is a top plan view of the micro structure shown inFIG. 2C (Embodiment Mode 1);

FIGS. 6A and 6B illustrate a structural example of a micro electromechanical device of the present invention; FIG. 6A is a cross-sectionalview of the micro electro mechanical device; and FIG. 6B is a top planview of the micro structure (Embodiment Mode 2);

FIGS. 7A to 7E are cross-sectional views showing a method formanufacturing a micro electro mechanical device of the present invention(Embodiment Mode 2);

FIGS. 8A to 8C are cross-sectional views showing a method formanufacturing a micro electro mechanical device of the present invention(Embodiment Mode 2);

FIG. 9 is a top plan view of a micro structure which is in the middle ofmanufacturing and is a top plan view of a first conductive layer (afirst sacrificial layer) (Embodiment Mode 2);

FIGS. 10A and 10B illustrate a structural example of a micro electromechanical device of the present invention; FIG. 10A is across-sectional view of the micro electro mechanical device; and FIG.10B is a top plan view of a micro structure (Embodiment Mode 3);

FIGS. 11A to 11E are cross-sectional views showing a method formanufacturing a micro electro mechanical device of the present invention(Embodiment Mode 3);

FIGS. 12A to 12C are cross-sectional views showing a method formanufacturing a micro electro mechanical device of the present invention(Embodiment Mode 3);

FIG. 13 is a top plan view of a micro structure which is in the middleof manufacturing and is a top plan view of a first conductive layer (afirst sacrificial layer) (Embodiment Mode 3);

FIG. 14 is an external perspective view of a micro structure of thepresent invention (Embodiment Mode 4);

FIG. 15 is a top plan view of a micro structure of the present inventionwhich is processed into a shape such that a corner is rounded(Embodiment Mode 5); and

FIG. 16 is a block diagram showing a structural example of a microelectro mechanical device of the present invention (Embodiment Mode 6).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiment modes of the present invention are describedwith reference to the accompanying drawings. However, the presentinvention is not limited to description to be given below. Unlesschanges and modifications depart from the spirit and the scope of thepresent invention, they should be construed as being included therein.Therefore, the present invention should not be construed as beinglimited to the description of the embodiment modes and embodiment.

Note that elements having the same reference numerals denote the sameelements among different embodiment modes and repetitive descriptionthereof is omitted.

EMBODIMENT MODE 1

In this embodiment mode, a method for manufacturing a micro structureand an electric circuit which controls the micro structure over the samesubstrate and at the same time is described. FIGS. 1A and 1B illustratea structure of a MEMS of this embodiment mode; FIG. 1A is across-sectional view of the MEMS; and FIG. 1B is a top plan view of themicro structure. A cross-sectional view taken along a dash-dot line O-Pin FIG. 1B corresponds to the cross-sectional view of a micro structure11 in FIG. 1A. Note that in FIG. 1A, the left side is thecross-sectional view of a first region in which the micro structure isformed and the right side is the cross-sectional view of a second regionin which the electric circuit is formed. This point is similar tocross-sectional views shown in FIGS. 2A to 3B. In addition, in FIG. 1A,a cross-sectional structure of an electric circuit 10 of the secondregion typically shows a transistor and other embodiment modes are alsosimilar in this respect.

The electric circuit 10 and the micro structure 11 are provided over thesame substrate 100 having an insulating surface. A transistor of theelectric circuit 10 is a thin film transistor and a structure thereof isa bottom-gate structure. The transistor includes a first conductivelayer 101, a first insulating layer 102 over the first conductive layer101, a semiconductor layer 103 over the first insulating layer 102, andsecond conductive layers 104 over the semiconductor layer 103.

The first conductive layer 101 forms a gate electrode or a gate wiringof the transistor. The first insulating layer 102 forms a gateinsulating layer. At least a channel formation region and ahigh-concentration impurity region functioning as a source region or adrain region are formed in the semiconductor layer 103. The secondconductive layers 104 are connected to the high-concentration impurityregion of the semiconductor layer 103 and functions as a sourceelectrode or a drain electrode.

A second insulating layer 105 is formed so as to cover the transistor.Third conductive layers 106 are formed over the second conductive layer105. The third conductive layers 106 are connected to the secondconductive layers 104 through a contact hole formed in the secondinsulating layer 105.

An electrode, a wiring, and a terminal of the electric circuit 10 areformed by using the first conductive layer 101, the second conductivelayers 104, and the third conductive layers 106. The micro structure 11and the electric circuit 10 are electrically connected by the electrodeand the wiring formed by using the first conductive layer 101, thesecond conductive layers 104, and the third conductive layers 106. Anelement other than the transistor is also formed in the electric circuit10. For example, a MIS-type capacitor or a diode can be formed by usingthe semiconductor layer 103.

As shown in FIG. 1A, the micro structure 11 is formed in an openingportion 107 formed in the second insulating layer 105. The microstructure 11 includes a movable electrode 121 (a first structurallayer), twelve fixed electrodes 122 (second structural layers) fixed tothe substrate 100, and wirings 123 connected to the fixed electrodes122. The movable electrode 121 is a so-called rotor and the fixedelectrode 122 is a so-called stator. Each of the wirings 123 isconnected to the electric circuit 10. Each of the wirings 123 and eachof the fixed electrodes 122 are integrated. That is, part of each of thewirings 123 forms each of the fixed electrodes 122. Therefore, each ofthe fixed electrodes 122 and each of the wirings 123 can be collectivelyconsidered as the second structural layer.

The movable electrode 121 is discoid. The movable electrode 121 isprovided with four opening portions 121a and is separated from thesubstrate 100.

The twelve fixed electrodes 122 are circularly provided so as tosurround the movable electrode 121. Although the fixed electrodes 122are fixed to the substrate 100, leading edges (edges which are close tothe movable electrode 121) thereof are separated from the substrate 100and electrostatic force can be set to operate on the movable electrode121 in a position separated from the substrate.

Each of the movable electrode 121, the fixed electrodes 122, and thewirings 123 has a multi-layer structure. A lower layer thereof is formedof an insulating layer and an upper layer thereof is formed of aconductive layer. The insulating layer of the lower layer is formed ofthe same insulating film and in the same layer as the first insulatinglayer 102. The conductive layer of the upper layer is formed of the samesemiconductor film and in the same layer as the semiconductor layer 103of the transistor

The micro structure 11 can function as a three-phase quadruple motor byconnecting the twelve fixed electrodes 122 in parallel every three fixedelectrodes by using the wirings 123. Electrostatic force (electrostaticattraction) is generated between the movable electrode 121 and each ofthe fixed electrodes 122 by sequentially applying voltage to each of thethree-phase fixed electrode 122. The movable electrode 121 is rotated bythis electrostatic force. A rotation direction of the movable electrode121 can be controlled by the voltage applied to each of the fixedelectrodes 122.

Hereinafter, a method for manufacturing the MEMS shown in FIGS. 1A and1B is described with reference to FIGS. 2A to 5. Here, the microstructure 11 is formed in the first region and the electric circuit 10is formed in the second region. First, a substrate having an insulatingsurface is prepared as the substrate 100. A conductive film is formedover the substrate 100 and is processed into predetermined shapes by aphotolithography process and an etching process, so that the firstconductive layer 101 and a first conductive layer 131 are formed asshown in FIG. 2A. That is, the first conductive layer 101 and the firstconductive layer 131 are formed by patterning the conductive film(Processing a film into predetermined shapes by a photolithographyprocess and an etching process is also called patterning). A firstinsulating layer 132 is formed over the first conductive layers 101 and131.

As the substrate having the insulating surface, an insulating substratesuch as a glass substrate, a quartz substrate, or a plastic substrate,or an insulating substrate in which an insulating film is formed over asurface can be used. In addition, a conductive substrate of a siliconwafer, metal, stainless steel, or the like in which an insulating filmis formed over a surface can also be used.

The insulating film which is formed over the surface of the substratecan be formed of a single-layer film or a multi-layer film of a materialselected from silicon oxide, silicon nitride, silicon oxynitride(SiO_(x)N_(y), x>y), silicon nitride oxide (SiO_(x)N_(y), x <y), and thelike. These films can be formed by CVD or sputtering. In the case of asilicon wafer or a metal substrate, nitride or oxide can also be formedby nitriding or oxidizing a surface thereof.

As a material of each of the first conductive layers 101 and 131, ametal such as molybdenum (Mo), tungsten (W), chromium (Cr), tantalum(Ta), titanium (Ti), or aluminum (Al), a metal compound which includesany of these metal elements as a main component (e.g., titanium nitrideor tungsten nitride), an alloy which includes any of these metalelements as a main component (e.g., an alloy of aluminum and titanium oran alloy of chromium and molybdenum), or the like can be selected. Thesematerials can be formed by vapor deposition or sputtering, and each ofthe first conductive layers 101 and 131 is formed of a single-layer filmor a multi-layer film of these materials.

The conductive layer 131 is a layer serving as a sacrificial layer, andshapes of the structural layers (the movable electrode 121, the fixedelectrodes 122, and the wirings 123) of the micro structure 11 aredefined by a shape of the first conductive layer 131. The firstconductive layer 131 is formed to be discoid as shown in FIG. 4. Anelectrode, a wiring, a terminal, or the like which forms the electriccircuit 10 can be formed in the electric circuit 10 by the firstconductive layer 101 as well as the gate electrode (the gate wiring).

In order to form a gate insulating film of the transistor, a materialwhich is suitable for the gate insulating film is selected as the firstinsulating layer 132. For example, the first insulating layer 132 can beformed of a single-layer film or a multi-layer film of a materialselected from silicon oxide, silicon nitride, silicon oxynitride(SiO_(x)N_(y), x>y), silicon nitride oxide (SiO_(x)N_(y), x<y), and thelike.

Next, a semiconductor layer 133 is formed over the first insulatinglayer 132. The semiconductor layer 133 can be formed of silicon,germanium, or a compound of silicon and germanium (silicon germanium).In addition, the semiconductor layer 133 is formed of a crystallinesemiconductor in this embodiment mode. An amorphous semiconductor isformed by CVD or sputtering and an amorphous semiconductor film iscrystallized by light energy or thermal energy, so that a crystallinesemiconductor film can be formed. Further, a microcrystallinesemiconductor or a polycrystalline semiconductor can also be formed byCVD or sputtering. In the later case, crystallization (or improvement incrystallinity) can also be performed by light energy or thermal energyafter the formation.

For example, in order to form amorphous silicon, it is only necessary toform amorphous silicon by CVD by using a source gas in which silane(SiH₄) gas is diluted by adding hydrogen. Alternatively, amorphoussilicon can be formed by sputtering by using a target formed of silicon.In order to form amorphous germanium, amorphous germanium can be formedby CVD by using a source gas in which germane (GeH₄) gas is diluted byadding hydrogen or can be formed by sputtering by using a target formedof germanium. In order to form amorphous silicon germanium, amorphoussilicon germanium can be formed by CVD by using a source gas in whichsilane (SiH₄) gas and germane (GeH₄) gas are mixed at a predeterminedratio and are diluted by adding hydrogen or can be formed by sputteringby using two kinds of targets formed of silicon and germanium.

Helium gas, fluorine gas, or a rare gas such as Ar, Kr, or Ne can beadded to a source gas as well as hydrogen gas for formation by CVD. Inaddition, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like can be usedas a source gas instead of monosilane (SiH₄.). Further, amicrocrystalline semiconductor or a polycrystalline semiconductor can bedirectly formed on the first insulating layer 132 by plasma CVD by usingthe above-described source gas. Furthermore, a microcrystallinesemiconductor or a polycrystalline semiconductor can be formed bycontrolling substrate temperature or the like by using theabove-described target.

As a crystallizing method of the amorphous semiconductor film,irradiation with laser light, irradiation with infrared rays or thelike, heating in an electric furnace, introduction of a metal elementwhich promotes crystallization of a semiconductor into a semiconductorfilm, or the like can be given.

As a laser which is used for crystallization, both a continuous wavelaser (a CW laser) and a pulsed laser can be used. As a gas laser whichis suitable for crystallization, an Ar laser, a Kr laser, an excimerlaser, or the like is given. As a solid-state laser, a laser using acrystal such as YAG, YVO₄, YAlO₃, GdVO₄, or forsterite (Mg₂SiO₄) whichincludes a dopant (e.g., Nd, Yb, Cr, Ti, Ho, Er, Tm, or Ta) as a medium,a glass laser, a ruby laser, an alexandrite laser, a Ti:sapphire laser,or the like can be given.

For crystallization of the semiconductor, not only irradiation with afundamental wave of a beam emitted from such a laser but alsoirradiation with a beam of a second harmonic wave to a fourth harmonicwave of the fundamental wave can be performed. For example, a secondharmonic wave (532 nm) or a third harmonic wave (355 nm) of an Nd:YVO₄laser (having a fundamental wave of 1064 nm) can be used. Energy densityof the laser is necessary to be set in a range of greater than or equalto 0.01 MW/cm² and less than or equal to 100 MW/cm², and preferably,energy density thereof is set in a range of greater than or equal to 0.1MW/cm² and less than or equal to 10 MW/cm². It is only necessary to setscan speed in a range of greater than or equal to 10 cm/sec and lessthan or equal to 200 cm/sec.

Note that a solid-state laser using the above-described crystal such asYAG as a medium, an Ar ion laser, and a Ti:sapphire laser can becontinuously oscillated, and can also be pulsed oscillated with arepetition rate of 10 MHz or more by performing a Q-switch operation,mode locking, or the like. When a laser beam is emitted with arepetition rate of 10 MHz or more, a semiconductor film can beirradiated with the next pulse during the period in which thesemiconductor film is melted by the laser beam and solidified.Therefore, a solid-fluid interface generated by performing irradiationwith the laser beam can be continuously moved by scanning the laserbeam, so that crystal grains of the semiconductor can be grown long inthe scan direction.

Alternatively, the semiconductor film can be crystallized by performingirradiation with infrared light, visible light, or ultraviolet lightwhich uses a lamp as a light source instead of the laser beam. As thelamp, a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbonarc lamp, a high pressure sodium lamp, or high pressure mercury lamp istypically used. Irradiation with light by the lamp is repeated 1 to 10times, preferably, 2 to 6 times. The lamp is turned on for 1 to 60seconds, preferably, 30 to 60 seconds for one irradiation, and asemiconductor film is to be heated at a temperature of 600° C. to 1000°C. for a moment.

In the case of using an electric furnace for heat treatment, it ispreferable that a heating process at around 400° C. be performed firstto release hydrogen in silicon, and then, temperature be raised totemperature to crystallize amorphous silicon when the semiconductor isamorphous silicon in which silane is used as source gas. By performingsuch heat treatment, roughness of the film in crystallization can besuppressed.

As a formation method of the crystalline semiconductor, there is amethod of performing crystallization using a metal element whichpromotes crystallization. This method is particularly preferable forcrystallizing an amorphous silicon film. A metal element which promotescrystallization of the amorphous silicon film is introduced into asemiconductor and irradiation with a laser beam or heat treatment by anelectric furnace at a temperature of 500° C. to 600° C. is performed, sothat a crystalline semiconductor having high continuity of a crystalgrain in a grain boundary can be obtained. As a metal element whichpromotes crystallization of silicon, one or a plurality of metalelements selected from iron (Fe), nickel (Ni), cobalt (Co), ruthenium(Ru), rhodium(Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum(Pt), copper (Cu), and gold (Au) can be used. In addition,crystallization using the metal element can be applied not only toamorphous silicon but also to amorphous silicon germanium includinggermanium at around 0.01 to 4.5 atomic %.

A means for introducing such a metal element into the semiconductor isnot particularly limited as long as it is a method in which the metalelement can be over a surface of the semiconductor or inside of thesemiconductor. For example, sputtering, CVD, plasma treatment (includingplasma CVD), an adsorption method, or a method of applying a solution ofmetal salt can be used. Among them, the method of using a solution iseasy and can easily adjust concentration of the metal element which isintroduced into the semiconductor. In order to spread the solution overthe entire surface of the semiconductor for applying the solution, it ispreferable to improve wettability of the surface of the semiconductor.In order to improve wettability thereof, it is preferable to form anextremely thin oxide film having a thickness of 10 nm or less over thesurface of the semiconductor. Such an extremely thin oxide film can beformed by performing irradiation with UV light in an oxygen atmosphere,thermal oxidation, treatment using hydrogen peroxide, treatment usingozone water including hydroxyl radical, or the like.

As for crystalline silicon which is crystallized by using the metalelement, the bond of elements of silicon in a crystal grain boundary iscontinued without breakage, similarly to single-crystalline silicon.Because of a characteristic of such a crystal structure, toughness ofcrystalline silicon becomes higher than that of polycrystalline siliconwhich is manufactured by performing crystallization without using ametal element. This is because stress concentration caused by a defectof the crystal grain boundary does not occur so that fracture toughnessof crystalline silicon becomes higher than that of polycrystallinesilicon which is manufactured by performing crystallization withoutusing the metal element. In addition, since electron mobility is highbecause the bond of atoms in the crystal grain boundary is continued,crystalline silicon is suitable for a material of a structural layer ofa micro structure which is controlled by electrostatic force(electrostatic attraction). Needless to say, such crystalline siliconcan be applied to a micro structure which is controlled byelectromagnetic force.

In addition, silicide is formed by connecting the metal element such asnickel used for crystallization to silicon. It is known that a metalcompound such as nickel silicide has higher intensity than that ofsilicon. Therefore, the metal element may be introduced so that silicideis formed in the structural layer.

On the other hand, since the metal element used for crystallizationdeteriorates element characteristics of the electric circuit 10, it ispreferable to remove the introduced metal element after crystallizationfrom the semiconductor layer 133 in the region (the second region) wherethe electric circuit 10 is at least formed. A method thereof isdescribed below.

First, a barrier layer formed of an oxide film (called chemical oxide)is formed having a thickness of 1 nm to 10 nm over a surface of thecrystalline semiconductor film by processing the surface of crystallinesilicon with a solution including ozone (typically, ozone water). Thebarrier layer functions as an etching stopper when only a getteringlayer is selectively removed in a later step.

Subsequently, the gettering layer including a rare gas element is formedover the barrier layer as a gettering site. Here, a semiconductor filmincluding a rare gas element is formed as the gettering layer by CVD orsputtering. When the gettering layer is formed, a sputtering conditionis adjusted appropriately so that the rare gas element is added to thegettering layer. As the rare gas element, one or a plurality of elementsselected from helium (He), neon (Ne), argon (Ar), krypton (Kr), andxenon (Xe) can be used. Note that since a metal element tends to move toa region having high oxygen concentration in gettering, it is preferablethat concentration of oxygen included in the gettering layer be, forexample, 5×10¹⁸ cm⁻³ or more.

Next, the metal element is removed from crystalline silicon byperforming heat treatment (e.g., heat treatment by an electric furnaceor irradiation with a laser beam) to the crystalline silicon film, thebarrier layer, and the gettering layer, so that concentration of themetal element in the crystalline silicon film can be decreased.

Next, as shown in FIG. 2C, a photolithography process and an etchingprocess are performed to the semiconductor layer 133 and the firstinsulating layer 132 to be processed into predetermined shapes. Thesemiconductor layer 103 of the transistor, a semiconductor layer 134serving as part of the first structural layer, and a semiconductor layer135 serving as part of the second structural layer are formed from thesemiconductor layer 133. In addition, the first insulating layer 132 isprocessed into the same shape as each of the semiconductor layers 103,134, and 135; the first insulating layer 102 serving as the gateinsulating film of the transistor is formed in the second region; and aninsulating layer 126 serving as part of the first structural layer andan insulating layer 127 serving as part of the second structural layerare formed in the first region. FIG. 5 is a top plan view of the microstructure 11 in FIG. 2C. A cross section taken along a dash-dot line O-Pin FIG. 5 is shown in FIG. 2C.

By this step, shapes of the first and second structural layers of themicro structure 11 are determined. A layered product of the insulatinglayer 126 and the semiconductor layer 134, which is formed circularly,forms the movable electrode 121, and a layered product of the insulatinglayer 127 and the semiconductor layer 135 forms the fixed electrode 122and the wiring 123. Note that the movable electrode 121 is the firststructural layer which is not fixed to the substrate 100 and is finallyseparated from the substrate 100. Therefore, all of the layered productof the insulating layer 126 and the semiconductor layer 134 is providedover a top surface of the first conductive layer 131 serving as thesacrificial layer. In addition, as shown in FIG. 5, the first structurallayer which is formed circularly may include opening portions 134 a. Thefixed electrode 122 is the second structural layer including a portionwhich is separated from the substrate 100 on edge and a portion which isfixed to the substrate 100. In order to form such a fixed electrode 122,an edge of the layered product of the insulating layer 127 and thesemiconductor layer 135 is formed so as to cover the top surface and aside surface of the first conductive layer 131, and other parts of thelayered product of the insulating layer 127 and the semiconductor layer135 are formed so as to be in contact with the surface (the insulatingsurface) of the substrate 100.

Next, as shown in FIG. 2D, in order to form an n-type or p-type highconcentration impurity region, an impurity which imparts conductivity isselectively added to the semiconductor layer 103 by doping or ionimplantation. Phosphorus (P) or arsenic (As) is used as the impurityelement which imparts n-type conductivity and boron (B) is used as theimpurity element which imparts p-type conductivity. In order to add theimpurity to portions except for a portion over the first conductivelayer 101 serving as the gate electrode, it is only necessary to add theimpurity by covering a region to which the impurity is not added with aresist mask by using photolithography. By this step, high concentrationimpurity regions 103b are formed in the semiconductor layer 103 and theregion over the first conductive layer 101 to which the impurity is notadded is determined as a channel formation region 103 a.

In addition, in the first region, an impurity is similarly added to thesemiconductor layer 134 which forms the first structural layer and thesemiconductor layer 135 which forms the second structural layer toimpart conductivity, so that conductive layers 128 and 129 are formed.Thus, the first structural layer can function as the movable electrode121 and the second structural layer can function as the fixed electrode122 and the wiring 123.

Next, a conductive film is formed by sputtering or the like and isprocessed by a photolithography process and an etching process, so thatthe second conductive layers 104 are formed in the second region and asecond conductive layer 137 is formed in the micro structure 11 as shownin FIG. 2E. An electrode, a wiring, a terminal, or the like which formsthe electric circuit 10 by the second conductive layers 104 is formed inthe second region as well as an electrode (a wiring) which is connectedto the high concentration impurity regions 103 b.

The second conductive layer 137 is formed in the first region to protectthe first and second structural layers from being removed by etchingwhen an opening portion 107 is formed in the second insulating layer105, which is described below. In addition, since the second conductivelayer 137 is finally removed, it is also a sacrificial layer (a secondsacrificial layer). The second conductive layer 137 covers at least aportion of the structural layers (126 to 129) in which the openingportion 107 is formed. Needless to say, there may be a portion in whicha portion of a region, where the second insulating layer 105 is left, iscovered in the structural layers (126 to 129). In this case, the wirings123 of the micro structure 11 partially include a stacked-layerstructure of the insulating layer 127, the conductive layer 129, and thesecond conductive layer 137.

In addition, the same materials as the first conductive layers 101 and131 can be selected as materials of the second conductive layers 104 and137, and the second conductive layers 104 and 137 are formed of asingle-layer film or a multi-layer film of these materials. Note thatsince the second conductive layer 137 is formed so as to cover theconductive layers 128 and 129 which are formed of semiconductors, it ispreferable to use a material including an metal element which can form ametal compound by reacting with silicon or germanium as the secondconductive layer 137. As such a metal element, a refractory metal suchas tungsten, titanium, molybdenum, or tantalum, cobalt, nickel, or thelike can be given.

In this case, the second conductive layer 137 reacts with a metalelement by performing heat treatment after the second conductive layer137 is formed, so that the conductive layers 128 and 129 can be layerswhich are formed of metal compounds. If the conductive layers 128 and129 are formed of silicon, they can be silicide layers. The conductivelayers 128 and 129 are formed to be metal compounds such as silicide, sothat both conductivity and intensity can be improved. Alternatively, theconductive layers 128 and 129 can partially be formed of metalcompounds. As heat treatment for forming the metal compounds, heattreatment by an electric furnace or irradiation with a laser beam orlamp light can be used.

In the case where necessary electric conductivity can be obtained byforming the conductive layers 128 and 129 to be the metal compounds suchas silicide, it is not necessary to add the n-type or p-type impurity tothe semiconductor layers 134 and 135 in the step in FIG. 2D.

Next, as shown in FIG. 3A, the second insulating layer 105 is formed. Inthe second region, a conductive film is formed over the secondconductive layers 104 after a contact hole is formed in the secondinsulating layer 105, and this conductive film is processed into apredetermined shape by a photolithography process and an etching processto form the third conductive layers 106 in the electric circuit 10. Awiring or the like other than a wiring connected to the transistor isalso formed in the electric circuit 10 by the third conductive layers106.

The second insulating layer 105 is an interlayer insulating film whichseparates the third conductive layers 106 from the second conductivelayers 104 between the layers and can also function as a sealing layerwhich seals the electric circuit 10. As the second insulating layer 105,an inorganic insulating film of silicon oxide, silicon nitride, siliconoxynitride (SiO_(x)N_(y), x>y), silicon nitride oxide (SiO_(x)N_(y),x<y), or the like can be used. Alternatively, an organic resin film ofpolyimide, acryl, or the like or a film including siloxane may be used.An organic resin may be any of a photosensitive resin and anon-photosensitive resin. The second insulating layer 105 can be formedof a single-layer structure or a multi-layer structure of theseinsulating materials. For example, a first layer can be an inorganicinsulating film formed of silicon nitride and a second layer can be anorganic resin film formed of polyimide or the like. Note that siloxaneis a material which has a skeletal structure with the bond of silicon(Si) and oxygen (O), and as a substituent, an organic group (e.g., analkyl group or an aryl group) is used. As the substituent, a fluorogroup may also be used.

The third conductive layers 106 can be formed similarly to the firstconductive layers 101 and 131 or the second conductive layers 104 and137. Note that since the first conductive layer 131 and the secondconductive layer 137 are removed by etching, it is necessary to select amaterial which cannot be removed by an etching agent which removes thefirst conductive layer 131 and the second conductive layer 137 as thethird conductive layers 106.

After the third conductive layers 106 are formed, the opening portion107 is formed in a region of the second insulating layer 105 in 11 isformed by etching as shown in FIG. 3B to expose the second conductivelayer 137. At this time, since the micro structure 11 is protected bythe second conductive layer 137, a layer which is formed by using amaterial having a low etching selection ratio to the second insulatinglayer 105 may be formed in the micro structure 11. For example, the samematerial as the second insulating layer 105 may be used as the firstinsulating layers 126 and 127. In addition, the first structural layerwhich is the movable electrode 121 is not fixed to anywhere of thesubstrate 100 when sacrificial layer etching is performed. Ifsacrificial layer etching is performed in such a condition, there is apossibility that the first structural layer disappear. In order toprevent this, it is preferable that the opening portion 107 be providedover not all of the first region but part of the first region. Forexample, the opening portion 107 is formed in the same position as theopening portions 134a provided in the semiconductor layer 134 serving asthe first structural layer shown in FIG. 1 or is formed to be slightlywider than the opening portions 134 a.

Next, the second conductive layer 137 (the second sacrificial layer) andthe first conductive layer 131 (the first sacrificial layer) are removedby etching, that is, so-called sacrificial layer etching is performed.When sacrificial layer etching is terminated, the micro structure 11shown in FIG. 1A is completed. The opening portions 121 a formed in themovable electrode 121 are provided so that an etching agent spreads overthe first sacrificial layer 131 when sacrificial layer etching isperformed. Any of wet etching and dry etching can be used for an etchingmethod of the second conductive layer 137 and the first conductive layer131, and a suitable etching agent is selected depending on the materialwhich forms the layers.

Foe example, when the first conductive layer 131 and the secondconductive layer 137 (the sacrificial layers) are formed of tungsten(W), a solution in which 28% ammonia and 31% hydrogen peroxide water aremixed in a ratio of one to two can be used as the etching agent. Whenthese sacrificial layers are formed of aluminum, mixed acid of nitricacid and phosphoric acid can be used as the etching agent.

In addition, depending on the material of the sacrificial layers,sacrificial layer etching can also be performed by dry etching using agas of F₂ or XeF₂ in a condition of high pressure such as atmosphericpressure.

Note that in order to prevent buckling of the micro structure by acapillary phenomenon in drying after wet etching, it is preferable toperform rinsing by using an organic solvent having low viscosity (e.g.,cyclohexane), drying in a condition of low temperature and low pressure,or treatment in which these are combined.

In this manner, in the present invention, the micro structure having therotor and the electric circuit can be formed over the same substratehaving the insulating surface. Therefore, mechanical intensity of aconnection portion of the electric circuit and the micro structure ishigh so that poor connection is hardly generated. In addition, sincethere is no step of integrating the micro structure and the electriccircuit later, manufacturing cost can be reduced.

EMBODIMENT MODE 2

In this embodiment mode, a method for manufacturing a micro structureand an electric circuit which controls the micro structure over the samesubstrate and at the same time is described. FIGS. 6A and 6B illustratea structure of a MEMS of this embodiment mode; FIG. 6A is across-sectional view of the MEMS; and FIG. 6B is a top plan view of themicro structure. Note that in FIG. 6A, the left side is thecross-sectional view of a first region in which the micro structure isformed and the right side is the cross-sectional view of a second regionin which the electric circuit is formed. Cross-sectional views shown inFIGS. 7A to 8C are also similar in this respect.

In the MEMS of this embodiment mode, an electric circuit 20 and a microstructure 21 are also provided over the same substrate 100. Although atransistor of the electric circuit 20 is a bottom gate thin filmtransistor, which is common to Embodiment Mode 1, a structure of asemiconductor layer 203 is different from that of Embodiment Mode 1.Although the micro structure 21 includes a rotor and a stator, which iscommon to Embodiment Mode 1, the micro structure 21 includes a rotationaxis (a third structural layer), which is different from EmbodimentMode 1. A structure of the MEMS of this embodiment mode is specificallydescribed with reference to FIGS. 6A and 6B.

The electric circuit 20 and the micro structure 21 are provided over thesame substrate 100 (over the same insulating surface). The thin filmtransistor of the electric circuit 20 includes the first conductivelayer 101 which forms a gate electrode or a gate wiring of thetransistor, the first insulating layer 102 which is provided over thefirst conductive layer 101 and forms a gate insulating layer, thesemiconductor layer 203 over the first insulating film 102, and thesecond conductive layers 104 over the semiconductor layer 203.

The semiconductor layer 203 is a two-layer structure and includes asemiconductor layer in which a channel formation region is formed and asemiconductor layer (a conductive layer) which have n-type or p-typeconductivity, which is stacked over the semiconductor layer andfunctions as a source region or a drain region (a high concentrationimpurity region). Hereinafter, the former is described as a firstsemiconductor layer and the latter is described as a secondsemiconductor layer. The second conductive layers 104 are formed overthe second semiconductor layer of the semiconductor layer 203, areconnected to the second semiconductor layer, and each function as asource electrode or a drain electrode.

The second insulating layer 105 is also formed in the electric circuit20 so as to cover the second conductive layers 104, the semiconductorlayer 203, the first insulating layer 102, and the first conductivelayer 101. The third conductive layers 106 are formed over the secondconductive layer 105. The third conductive layers 106 are connected tothe second conductive layers 104 through a contact hole formed in thesecond insulating layer 105.

An electrode, a wiring, and a terminal of the electric circuit 20 areformed by using the first conductive layer 101, the second conductivelayers 104, and the third conductive layers 106. An element other thanthe transistor is also formed in the electric circuit 20. For example, acapacitor can be formed by using an n-type semiconductor layer of thesemiconductor layer 203, the first insulating layer 102, and the firstconductive layer 101.

As shown in FIG. 6B, the micro structure 21 includes a movable electrode221 (a first structural layer), twelve fixed electrodes 222 (secondstructural layers) fixed to the substrate 100, wirings 223 connected tothe fixed electrodes 222, and a rotation axis 225 (a third structurallayer) which is fitted into a center of the movable electrode 221. Themovable electrode 221 is a so-called rotor and the fixed electrode 222is a so-called stator. The movable electrode 221 rotates around therotation axis 225 by electrostatic attraction generated between themovable electrode 221 and the fixed electrode 222 by sequentiallyapplying voltage to the three-phase fixed electrodes 222. A rotationdirection of the movable electrode 221 can be controlled by voltageapplied to the fixed electrodes 222.

The fixed electrodes 222 and the wirings 223 have the same structures asthe fixed electrodes 122 and the wirings 123 of Embodiment Mode 1,respectively except that a stacked-layer structure of the structurallayer which forms the electrode and the wiring is different, and each ofthe fixed electrodes 222 and each of the wirings 223 are integrated.Each of the fixed electrodes 222 and each of the wirings 223 can becollectively considered as the second structural layer.

The movable electrode 221 has a structure in which four T-shaped (ashape in which width of an edge is widened) layers are symmetricallyformed around a disk. In addition, seeing from a top surface, anappearance of the movable electrode 221 is a cross shape andcircumference of the movable electrode 221 is an arc-shaped.

Each of the movable electrode 221, the fixed electrodes 222, and thewirings 223 has a multi-layer structure. A lower layer thereof is formedof an insulating layer and an upper layer thereof is formed of asemiconductor layer. The insulating layer of the lower layer is formedof the same insulating film and in the same layer as the firstinsulating layer 102. The semiconductor layer of the upper layer has thesame two-layer structure of the first semiconductor layer and the secondsemiconductor layer (the conductive layer) as the semiconductor layer203, and is formed of the same semiconductor film and in the same layeras the semiconductor layer 203 of the transistor.

The rotation axis 225 is fixed to the substrate 100 through an openingportion which is formed in a central portion of the movable electrode221. In addition, an edge of the rotation axis 225 is formed to belarger than the opening portion of the movable electrode 221 and isformed so that the movable electrode 221 does not come out. Note that itis not necessary to provide the rotation axis 225 in the central of themovable electrode 221. In the case where the micro structure 21 is to beused as the rotor, the rotation axis 255 can be provided in other thanthe central.

Hereinafter, a method for manufacturing the MEMS shown in FIGS. 6A and6B is described with reference to FIGS. 7A to 9. Note that descriptionwhich overlaps with Embodiment Mode 1 is omitted and the description ofEmbodiment Mode 1 is employed.

First, similarly to Embodiment Mode 1, a substrate having an insulatingsurface is prepared as the substrate 100. Conductive films are formedover the substrate 100 and are processed into predetermined shapes by aphotolithography process and an etching process, so that the firstconductive layers 101 and 131 are formed as shown in FIG. 7A. The firstinsulating layer 132 is formed over the first conductive layers 101 and131.

Another electrode, wiring, or terminal is formed by the first conductivelayer 101 in the electric circuit 20 as well as the gate wiring of thetransistor. The first conductive layer 131 formed in the micro structure21 functions as a sacrificial layer and is processed into a discoidshape as shown in FIG. 4, similarly to Embodiment Mode 1.

Next, the semiconductor layer which forms the movable electrode 221, thefixed electrodes 222, and the wirings 223 is formed in the first regionand the semiconductor layer which forms the semiconductor layer 203 ofthe transistor is formed in the second region. First, as shown in FIG.7B, a semiconductor film 233A which forms the first semiconductor layeris formed. Since the semiconductor film 233A forms the channel formationregion of the transistor, the semiconductor film 233A is formedintentionally without being added with an impurity which impartsconductivity so that the semiconductor film 233A becomes an intrinsicsemiconductor (an i-type semiconductor). The semiconductor film 233A maybe any of an amorphous semiconductor and a crystalline semiconductorsuch as a micro crystalline semiconductor or a polycrystallinesemiconductor. As a method of forming the semiconductor film 233A, themethod described in Embodiment Mode 1 can be used.

Next, as shown in FIG. 7C, a semiconductor film 233B which forms thesecond semiconductor layer is formed. Since the semiconductor film 233Bforms the source region and the drain region of the transistor, thesemiconductor film 233B is a semiconductor layer including an impuritywhich imparts n-type or p-type conductivity and also functions as aconductive layer. The semiconductor film 233B may also be any of anamorphous semiconductor and a crystalline semiconductor such as a microcrystalline semiconductor or a polycrystalline semiconductor. As amethod of forming the semiconductor film 233B, the method described inEmbodiment Mode 1 can be used.

Since a semiconductor layer having a two-layer structure of thesemiconductor film 233A and the semiconductor film 233B is used as thestructural layer in this embodiment mode, the structural layer can beformed of a semiconductor layer of two layers which have differentcrystalline structures. A characteristic such as intensity is varieddepending on crystalline structures, a defect of the crystallinestructure of each layer can be compensated by forming the structurallayer using a multi-layer film of semiconductors having differentcrystalline structures.

For example, the semiconductor film 233A can be formed of an amorphoussemiconductor and the semiconductor film 233B can be formed of apolycrystalline semiconductor. Alternatively, the semiconductor film233A can be formed of a polycrystalline semiconductor and thesemiconductor film 233B can be formed of an amorphous semiconductor.

Needles to say, the semiconductor film 233A and the semiconductor film233B may have the same crystalline structure. By forming each of thesemiconductor layers with a multi-layer structure, it becomes easy toform the structural layer thickly. For example, formation of anamorphous semiconductor film and crystallization by performing heattreatment using thermal energy or light energy are repetitivelyperformed, so that a stacked-layer film in which crystallinesemiconductor films are stacked can be formed. Since the stacked-layerfilm of crystalline semiconductors can be formed in this manner andinternal stress of a lower layer can be relieved by performing heattreatment of a crystallization step of an upper layer, peeling of thefilm and transformation of the substrate can be prevented.

In addition, in the case where crystalline semiconductors are used asthe semiconductor film 233A and the semiconductor film 233B, thesemiconductor film 233A and the semiconductor film 233B can be stackedso that crystalline growth directions thereof are varied. For example,in the case of crystallizing the semiconductor films using a metalelement, crystalline growth of the semiconductors develops in a verticaldirection to the substrate when the metal element is added to the entiresurface of regions to be crystallized. On the other hand, in the case ofselectively adding a metal element and performing laser irradiation orheat treatment, crystalline growth of the semiconductors develops in aparallel direction to the substrate.

By stacking layers having different crystalline growth directions, astructural layer having excellent toughness can be formed. Since thelayers having the different crystalline growth directions are stacked, adefect of each layer can be compensated. That is, a crack is hardlyspread over the layer having the different crystalline growth directioneven when the crack is generated in a crystal grain boundary of onelayer, so that breaking of the structural layer can be suppressed.

In addition, the semiconductor films 233A and 233B can be crystallizedby selecting a region which is crystallized. That is, the semiconductorfilms 233A and 233B can be crystallized by selecting only the region(the second region) in which the electric circuit 20 is formed orselecting only the region (the first region) in which the microstructure 21 is formed. For example, the semiconductor film 233A isformed of an amorphous semiconductor and only the region to be the microstructure 21 is crystallized. The semiconductor film 233B is formed of amicro crystalline semiconductor and partial crystallization is notperformed. In this case, the first semiconductor layer of the microstructure 21 and the first semiconductor layer of the transistor havedifferent crystalline structures even when they are formed in the samelayer, and the second semiconductor layers of the micro structure 21 andthe transistor have the same crystalline structure.

Note that selective crystallization is achieved by selectivelyirradiating the semiconductors with a laser beam. In addition, in thecase of performing crystallization using the metal element, a region towhich the metal element is added is formed partially.

After the semiconductor films 233A and 233B are formed, thesemiconductor films 233A and 233B, and the first insulating layer 132are processed into predetermined shapes by a photolithography processand an etching process as shown in FIG. 7D.

First semiconductor layers 234A, 228A, and 229A are formed from thesemiconductor film 233A. Semiconductor layers 234B, 228B, and 229B areformed from the semiconductor film 233B. In addition, the firstinsulating layer 132 is removed except for portions which overlap withthe semiconductor layers 234A, 234B, 228A, 228B, 229A, and 229B by anetching process, and the first insulating layer 102, and firstinsulating layers 226 and 227 are formed in the second region and thefirst region, respectively.

By this step, shapes of the movable electrode 221, the fixed electrodes222, and the wirings 223 of the micro structure 21 are determined. FIG.9 is a top plan view of the micro structure 21 in FIG. 7D. A crosssection taken along a dash-dot line O-P in FIG. 9 is shown in FIG. 7D.

A layered product of the insulating layer 226, the first semiconductorlayer 228A, and the second semiconductor layer 228B is the structurallayer (the first structural layer) which forms the movable electrode221, and is provided with an opening portion 230 for forming therotation axis 225 in the center. A layered product of the firstinsulating layer 227, the first semiconductor layer 229A, and the secondsemiconductor layer 229B is the structural layer (the second structurallayer) which forms the fixed electrodes 222 and the wirings 223.

The first insulating layer 102 serving as the gate insulating film and asemiconductor layer 234 which forms the semiconductor layer 203 areformed in the second region. The semiconductor layer 234 is formed of astacked-layer film of the first semiconductor layer 234A and the secondsemiconductor layer 234B.

Next, a conductive film is formed by sputtering or the like and isprocessed by a photolithography process and an etching process, so thatthe second conductive layers 104 are formed in the second region and asecond conductive layer 237 is formed in the micro structure 21 as shownin FIG. 7E. An electrode, a wiring, a terminal and the like which formthe electric circuit 20 by the second conductive layers 104 are formedin the second region as well as an electrode (a wiring) of thetransistor. In addition, the conductive film which forms the secondconductive layers 104 and 237 can be formed similarly to Embodiment Mode1.

The second conductive layer 237 is formed to protect the structurallayers from being removed by etching when the opening portion 107 isformed in the second insulating layer 105, which is described below. Inaddition, since the second conductive layer 237 is finally removed, itis also a sacrificial layer (a second sacrificial layer). The secondconductive layer 237 covers at least surfaces of the structural layers(the first semiconductor layers 228A and 229A, the second semiconductorlayers 228B and 229B, and the insulating layers 226 and 227) in whichthe opening portion 107 is formed. Needless to say, there may be aportion which covers the structural layers (the first semiconductorlayer 229A, the second semiconductor layer 229B, and the insulatinglayer 227) in which the second insulating layer 105 is left. In thiscase, the wirings 223 of the micro structure 21 partially include astacked-layer structure of the insulating layer 227, the firstsemiconductor layer 229A, the second semiconductor layer 229B, and thesecond conductive layer 237.

The semiconductor layer 234 is partially removed by etching using thesecond conductive layers 102 as masks, so that the semiconductor layer203 is formed in the second region. The second semiconductor layer 234Bis divided by this etching and a pair of second semiconductor layers203B is formed. The pair of the second semiconductor layers 203Bfunctions as a source region and a drain region. An outer layer of thefirst semiconductor layer 234A is partially removed and a firstsemiconductor layer 203A in which a channel formation region is formedis formed.

On the other hand, the second conductive layer 237 is formed of metalwhich can form a metal compound by reacting with silicon or germanium,so that the first semiconductor layers 228A and 229A, and the secondsemiconductor layers 228B and 229B are reacted with the secondconductive layer 237 by performing heat treatment similarly toEmbodiment Mode 1; thus, a metal compound (typically, silicide which isa compound of metal and silicon) can be formed in the first region. Inthis case, formation of the metal compound by heat treatment or the likeis performed after the semiconductor layer 234 is etched.

In this case, all of the second semiconductor layers 228B and 229B canbe formed of the metal compound. Alternatively, outer layers of thesecond semiconductor layers 228B and 229B can be partially formed of themetal compound. The second semiconductor layers 228B and 229B areconductive layers having n-type or p-type conductivity and intensity aswell as electric conductivity thereof can be improved by forming thesecond semiconductor layers 228B and 229B to be the metal compound.

In addition, all of the first semiconductor layers 228A and 229A can beformed of the metal compound depending on thickness of the secondsemiconductor layers 228B and 229B. Certain thickness of sides which arein contact with the second conductive layer 237 can be at least formedof a metal compound. That is, sides of the movable electrode 221 and thefixed electrode 222 or inside of the opening portion 230 in which therotation axis is provided later can be formed of the metal compound.Forming such portions which are easily damaged to be the metal compoundsis extremely effective for improvement in intensity of the microstructure.

Further, since the first semiconductor layers 228A and 229A do notparticularly have conductivity because of formation of the channelformation region of the transistor, resistance in the movable electrode221, the fixed electrodes 222, and the wirings 223 can be lowered byforming the metal compound. In particular, since the metal compound isformed over a surface in which the fixed electrodes 222 are opposed tothe movable electrode 221, an area of a portion where electrostaticforce can be generated can be widened.

Note that electric conductivity of the first semiconductor layers 228Aand 229A is improved, so that the first semiconductor layers 228A and229A can be conductive layers. For example, it is only necessary to forman n-type or p-type impurity region by selectively adding an impuritywhich imparts n-type or p-type conductivity to a portion in the firstregion of the first semiconductor layer 233A before the secondsemiconductor layer 233B is formed (see FIG. 7B). Such a region isselectively formed of a metal compound (e.g., silicide or a compound ofgermanium and metal), so that the first semiconductor layers 228A and229A can also be the conductive layers. Alternatively, both addition ofthe impurity and formation of the metal compound can also be performed.

Next, as shown in FIG. 8A, the second insulating layer 105 is formed. Aconductive film is formed over the second conductive layers 104 after acontact hole is formed in the second insulating layer 105, and theconductive film is processed into a predetermined shape by aphotolithography process and an etching process to form the thirdconductive layers 106 in the electric circuit 20. As shown in FIG. 8B,the opening portion 107 is formed in a region in which the microstructure 21 of the second insulating layer 105 is formed by etching toexpose the second conductive layer 237.

Next, as shown in FIG. 8B, an opening portion 238 which penetrates thesecond conductive layer 237 and the first conductive layer 131 is formedin a portion in which the rotation axis 225 is formed. The openingportion 238 can be formed by dry etching and the second conductive layer237 and the first conductive layer 131 are formed by anisotropicetching.

The opening portion 238 is formed inside of the opening portion 230 ofthe movable electrode 221. In order to separate the rotation axis 225from the movable electrode 221, the opening portion 238 is formed to besmaller than the opening portion 230 which is provided in the movableelectrode 221 shown in FIG. 7D so that the second conductive layer 237is left in the opening portion 230.

A film formed of a polycrystalline semiconductor, metal, a metalcompound, an alloy, or the like is formed over the second conductivelayer 237 and is processed into a predetermined shape by aphotolithography process and an etching process to form the rotationaxis 225 as shown in FIG. 8C. A material which cannot be removed by anetching agent used for sacrificial layer etching which removes the firstconductive layer 131 and the second conductive layer 237 is used as amaterial of the rotation axis 225.

The edge (the portion over the second conductive layer 237) of therotation axis 225 is processed to be wider than the opening portion 230and a bottom of the rotation axis is formed so as to adhere to thesubstrate 100.

Next, the second conductive layer 237 (the second sacrificial layer) andthe first conductive layer 131 (the first sacrificial layer) are removedby etching, that is, so-called sacrificial layer etching is performed.When sacrificial layer etching is terminated, the micro structure 11shown in FIG. 6A is completed.

In this manner, in the present invention, the micro structure having therotor and the electric circuit can be formed over the same substratehaving the insulating surface. Therefore, mechanical intensity of aconnection portion of the electric circuit and the micro structure ishigh so that poor connection is hardly generated. In addition, sincethere is no step of integrating the micro structure and the electriccircuit later, manufacturing cost can be reduced.

EMBODIMENT MODE 3

In this embodiment mode, an example is described in which the microstructure is transformed in the MEMS of Embodiment Mode 1. In thisembodiment mode, a micro structure includes a mobile part (a slider)which is a comb-shape and long and fixed parts on opposite sides andmoves in a direction which is horizontal to the substrate. Such a microstructure changes a certain mechanical movement into another movement,for example, it changes a rotational movement into a linear movement.Specifically, as shown in FIG. 14, a comb of a mobile part 422 (aslider) engages with a cog of a gear 421 so that the gear 421 whichrotates moves the mobile part 422. The mobile part 422 moves linearly inits longitudinal direction. In addition, fixed parts 425 are provided onopposite ends of the mobile part 422 and limits the mobile part to movein directions other than the longitudinal direction. FIGS. 10A and 10Billustrate a structure of a MEMS of this embodiment mode; FIG. 10A is across-sectional view of the MEMS; and FIG. 10B is a top plan view of themicro structure. Note that in FIG. 10A, the left side is thecross-sectional view of a first region in which the micro structure isformed and the right side is the cross-sectional view of a second regionin which the electric circuit is formed. Cross-sectional views shown inFIGS. 11A to 12C are also similar in this respect. Further, thecross-sectional view taken along a dash-dot line O-P in FIG. 10Bcorresponds to the cross-sectional view of a micro structure 31 in FIG.10A. Note that since the micro structure 31 is long in a longitudinaldirection, only part of it is shown with a top and a bottom omitted.

In this embodiment mode, the electric circuit 10 and the micro structure31 are also provided over the same substrate 100 (over the sameinsulating surface). As shown in FIG. 10B, the micro structure 31includes a comb-shaped mobile part 321 (a first structural layer), apair of rectangular first fixed parts 322 (a second structural layer),and wirings 323 and second fixed parts 325 which are connected to thefirst fixed parts 322. The wirings 323 and the first fixed parts 322 areintegrated and are electrically connected to the electric circuit 10. Inaddition, since the mobile part 321 (the first structural layer) doesnot move in a direction which is perpendicular to the substrate, themobile part 321 may include the second fixed parts 325.

The mobile part 321 is a comb-shaped electrode and is formed so as to beseparated from the substrate 100. The pair of the first fixed parts 322is rectangular electrodes and is provided so as to sandwich the mobilepart 321. Although the first fixed parts 322 are formed so as to befixed to the substrate, edges of the first fixed parts 322 which areopposite to the mobile part 321 are separated from the substrate 100.The second fixed parts 325 are formed so as to adhere to the first fixedparts 322. In addition, edges of the second fixed parts 325 areseparated from the first fixed parts 322 and overlap with the mobilepart 321.

In the micro structure 31, the pair of the first fixed parts 322 islayers which limit their movements so as not to move in a directionwhich is different from a direction in which the mobile part 321 moves(here, the longitudinal direction of the mobile part).

In this embodiment mode, since the structure of the electric circuit 10is the same as that of Embodiment Mode 1, a stacked-layer structure ofthe mobile part 321, the first fixed parts 322, and the wirings 323 arethe same as the stacked-layer structure of the first structural layer(the movable electrode 121) and the second structural layer (the fixedelectrodes 122 and the wirings 123).

Hereinafter, a method for manufacturing the MEMS of this embodiment modeis described with reference to FIGS. 11A to 13. Note that descriptionwhich overlaps with Embodiment Mode 1 is omitted and the description ofEmbodiment Mode 1 is employed.

Similarly to Embodiment Mode 1, a substrate having an insulating surfaceis prepared as the substrate 100. A conductive film is formed over thesubstrate 100 and is processed into a predetermined shape by aphotolithography process and an etching process, so that the firstconductive layer 101 is formed in the second region and a firstconductive layer 331 is formed in the first region as shown in FIG. 11A.The first insulating layer 132 is formed over the first conductivelayers 101 and 331. The first conductive layer 331 functions as asacrificial layer (a first sacrificial layer) and is processed into arectangular shape as shown in FIG. 13. Note that that FIG. 13 is a topplan view of the micro structure 31 in FIG. 11C, and a cross sectiontaken along a dash-dot line O-P in FIG. 13 is shown in FIG. 11C.

Next, as shown in FIG. 11B, a layer which forms the mobile part 321 andthe first fixed parts 322 is formed in the first region and asemiconductor layer 333 which forms the semiconductor layer 103 of atransistor is formed in the second region.

Next, as shown in FIG. 11C, the semiconductor layer 333 and the firstinsulating layer 132 are processed into predetermined shapes by aphotolithography process and an etching process. The semiconductor layer103 of the transistor is formed from the semiconductor layer 333 in thesecond region. In addition, a semiconductor layer 334 serving as part ofthe first structural layer and semiconductor layers 335 serving as partsof the second structural layer are formed in the first region. Further,the first insulating layer 132 is processed into the same shape as eachof the semiconductor layers 103, 334, and 335; the first insulatinglayer 102 serving as a gate insulating film of the transistor is formedin the second region; and insulating layers 326 and 327 are formed inthe first region.

By this step, shapes of the first and second structural layers of themicro structure 31 are determined. A layered product of the insulatinglayer 326 and the semiconductor layer 334 forms the mobile part 321 (thefirst structural layer), and a layered product of the insulating layer327 and the semiconductor layer 335 forms the first fixed part 322 andthe wiring 323 (the second structural layer). As shown in FlG. 13, thesemiconductor layer 334 is formed with a rectangular shape having acomb-shaped portion, and each of the semiconductor layers 335 has astructure in which a rectangular portion serving as the first fixed part322 and a linear portion serving as the wiring 323 are integrated and isprovided so as to sandwich the semiconductor layer 334.

Note that since the mobile part 321 is finally separated from thesubstrate 100, all of the layered product of the insulating layer 326and the semiconductor layer 334 is provided over a top surface of thefirst conductive layer 331. In addition, in order to form a portionwhich is separated from the substrate 100 on edge of the first fixedpart 322 and fix the first fixed part 322 to the substrate 100, an edgeof the layered product of the insulating layer 327 and the semiconductorlayer 335 is formed so as to cover the top surface and a side surface ofthe first conductive layer 331, and other parts of the layered productof the insulating layer 327 and the semiconductor layer 335 are formedso as to be in contact with the surface (the insulating surface) of thesubstrate 100.

An impurity which imparts n-type or p-type conductivity is selectivelyadded to the semiconductor layers 103, 334, and 335 by doping or ionimplantation. In order to selectively add the impurity to portionsexcept for a portion over the first conductive layer 101 serving as agate electrode, a resist mask is formed over a portion to which theimpurity is not added by using photolithography and the impurity isadded by using this mask. By this step, as shown in FIG. 11D, the highconcentration impurity regions 103 b are formed in the semiconductorlayer 103 and the region of the semiconductor layer 103 to which theimpurity is not added is determined as the channel formation region 103a. The high concentration impurity regions 103 b each function as asource region or a drain region. In addition, in the case of not forminga resist mask over the structural layers, the semiconductor layers 334and 335 which form the structural layers have conductivity by additionof the impurity, so that conductive layers 328 and 329 are formed. Sinceit is not necessary that the structural layers have conductivity in thisembodiment mode, a resist mask is formed over the structural layers sothat the impurity is not added to the structural layers.

Next, a conductive film is formed by sputtering or the like and isprocessed by a photolithography process and an etching process, so thatthe second conductive layers 104 are formed in the second region and asecond conductive layer 337 (a second sacrificial layer) is formed inthe first region as shown in FIG 11E. The second conductive layers 104each function as a source region or a drain region.

The second conductive layer 337 is formed to protect the first andsecond structural layers from being removed by etching when an openingportion 107 is formed in the second insulating layer 105. Therefore, itis not necessary that the second conductive layer 337 cover all of thestructural layer (328 and 329) and it is only necessary that the secondconductive layer 337 cover at least a portion of the structural layer(328 and 329) in which the opening portion 107 is formed. In addition,the second conductive layer 337 also functions as a sacrificial layerfor forming a gap between the first fixed part 322 and the second fixedpart 325.

Alternatively, when it is necessary that the structural layers haveconductivity, the second conductive layer 337 is formed of a materialincluding a metal element which can form a metal compound by beingreacted with silicon or germanium as described in Embodiment Mode 1, sothat each of the conductive layers 328 and 329 can be formed of a metalcompound (typically, silicide).

Next, as shown in FIG. 12A, the second insulating layer 105 is formed. Aconductive film is formed over the second conductive layers 104 after acontact hole is formed in the second insulating layer 105, and theconductive film is processed into a predetermined shape by aphotolithography process and an etching process to form the thirdconductive layers 106 in the second region. After the third conductivelayers 106 are formed, the opening portion 107 is formed in the secondinsulating layer 105 in the first region by etching as shown in FIG.12B. Then, the second conductive layer 337 (the second sacrificiallayer) and the first conductive layer 331 (the first sacrificial layer)are removed by etching, that is, so-called sacrificial layer etching isperformed. The mobile part 321 is not fixed to the substrate 100 whenthe sacrificial layers (337 and 331) are removed, similarly to themovable electrode of the micro structure in Embodiment Mode 1.Therefore, the opening portion 107 can also be formed so that the secondinsulating layer 105 is left over the mobile part 321, similarly toEmbodiment Mode 1. Further, the second fixed part can also be formedover the mobile part 321. Here, an example of forming the second fixedpart is described.

Next, in order to connect the first fixed parts 322 and the second fixedparts 325, the second conductive layer 337 is partially removed by aphotolithography process and an etching process (see FIG. 12B).

A conductive film is formed over the second conductive layer 237 and isprocessed into a predetermined shape by a photolithography process andan etching process to form the second fixed parts 325 (the thirdstructural layer) as shown in FIG. 12C. Parts of the second fixed parts325 are formed so as to be fixed to the first fixed parts 322 andconnected to the first fixed parts 322. The edges of the second fixedparts 325 are provided so as to be separated from the first fixed parts322 and overlap with the mobile part 321.

As a material of each of the second fixed parts 325, a metal such asmolybdenum (Mo), tungsten (W), chromium (Cr), tantalum (Ta), titanium(Ti), or aluminum (Al), a metal compound which includes any of thesemetal elements as a main component (e.g., titanium nitride or tungstennitride), an alloy which includes any of these metal elements as a maincomponent (e.g., an alloy of aluminum and titanium or an alloy ofchromium and molybdenum), or the like can be selected. Alternatively,silicide of a refractory metal such as tungsten, titanium, molybdenum,or tantalum, cobalt, nickel, or the like, crystalline silicon havingn-type or p-type conductivity, or the like can also be used. Each of thesecond fixed parts 325 is a conductive film formed by using a materialselected from these conductive materials with a single layer or a multilayer. In addition, when it is not necessary that each of the secondfixed parts 325 have conductivity, each of the second fixed parts 325 isformed by using an insulating material with a single layer or a multilayer. Note that a material which cannot be removed by an etching agentused for sacrificial layer etching which removes the first conductivelayer 331 and the second conductive layer 337 is used as a material ofeach of the second fixed parts 325.

Next, the second conductive layer 337 (the second sacrificial layer) andthe first conductive layer 331 (the first sacrificial layer) are removedby etching, that is, so-called sacrificial layer etching is performed.When sacrificial layer etching is terminated, the micro structure 31shown in FIG. 10A is completed.

In this manner, in the present invention, the micro structure having therotor and the electric circuit can be formed over the same substratehaving the insulating surface. Therefore, mechanical intensity of aconnection portion of the electric circuit and the micro structure ishigh so that poor connection is hardly generated. In addition, sincethere is no step of integrating the micro structure and the electriccircuit later, the structure of the MEMS is simplified so thatmanufacturing cost can be reduced.

Although the mobile part 321 (the first structural layer) has the combshape in this embodiment mode, it can also be processed into a shapewhich functions as the rotor or the gear or a shape which functions asthe slider. It is only necessary that the first structural layer beprocessed into a movable shape and the shape of the first structurallayer is not limited to the shape of this embodiment mode.

Further, although the electric circuit 10 of Embodiment Mode 1 is usedas the structure of the electric circuit in this embodiment mode, theelectric circuit 20 of Embodiment Mode 2 can also be used as thestructure of the electric circuit. In this case, a stacked-layerstructure of the mobile part 321 and the first fixed part 322 (the firstand second structural layers) is similar to that of the first and secondstructural layers (the movable electrode 221 and the fixed electrode222) of Embodiment Mode 2.

EMBODIMENT MODE 4

In this embodiment mode, a structural example of a micro structure isdescribed. FIG. 14 is an external perspective view of the microstructure of this embodiment mode. Although only the micro structure isshown in FIG. 14, an electric circuit and the micro structure areintegrated over a substrate having an insulating surface.

The micro structure includes the first mobile part 421 (a firststructural layer) having a gear shape, the second mobile part 422 (asecond structural layer) having a cog which engages with the firstmobile part 421, and the fixed parts 425 for operating electrostaticforce or the like on the second mobile part 422. The fixed parts 425 areelectrically connected to the electric circuit which is not shown.

The first mobile part 421 is a gear and is separated from the substrate(the insulating surface) and other structural layers, similarly to thefirst structural layers of other embodiment modes. The second mobilepart 422 is a slider and includes the cog which engages with the firstmobile part 421. The second mobile part 422 is also separated from thesubstrate and other structural layers, similarly to the first structurallayer. The first structural layer 421 engages with the second structurallayer 422 in this manner, so that a linear movement of the firststructural layer 421 can be changed into a rotational movement of thesecond structural layer 422. On the contrary, the rotational movement ofthe second structural layer 422 can be changed into the linear movementof the first structural layer 421.

For example, the second structural layer 422 can move linearly byutilizing the fixed parts 425. When electrostatic force is operated onthe second mobile part 422 by applying voltage between the fixed parts425 and the second structural layer 422, the second mobile part 422moves horizontally like an electrostatic linear motor and the firstmobile part 421 rotates. Note that the second mobile part 422 can alsobe moved by not electrostatic force but electromagnetic force. Such amicro structure can be used as a manipulator which deals with a smallcell. Further, the micro structure can be a micro structure whichrotates the first mobile part 421 and changes a rotational movement ofthe first structural layer 421 into a horizontal movement of the secondstructural layer 422 as shown in Embodiment Modes 1 and 2.

The micro structure shown in FIG. 14 shows an example in which the microstructure is formed by employing the method for manufacturing the MEMSof Embodiment Mode 3. The first to third structural layers (421, 422,and 425) of the micro structure are formed over the substrate 100 at thesame time as the electric circuit 10. By changing the shapes of thefirst to third structural layers (the mobile part 321, the first fixedparts 322, and the second fixed parts 325) and the shapes of the firstand second sacrificial layers (the first conductive layer 331 and thesecond conductive layer 337) in Embodiment Mode 3, the micro structureof this embodiment mode can be manufactured. Therefore, a stacked-layerstructure of each structural layer of the micro structure is similar tothat of the micro structure 31, which is a stacked layer of aninsulating layer and a semiconductor layer.

Further, a structure of the electric circuit can also be the electriccircuit 20 of Embodiment Mode 2. In this case, the stacked-layerstructure of each of the first to third structural layers (421, 422, and425) is similar to the stacked-layer structure of each of the first tothird structural layers (221, 222, and 225) of Embodiment Mode 2.

EMBODIMENT MODE 5

In this embodiment mode, a technique for making a movable portion of amicro structure smoothly move is described.

The micro structure 11 of Embodiment Mode 1 is described as an example.Although FIG. 1A shows that the movable electrode 121 (the firststructural layer) and the substrate 100 are separated in order to easilyunderstand the structure of the micro structure, the movable electrode121 does not float from the substrate 100 but is in contact with thesubstrate by gravity after sacrificial layer etching. Therefore,friction between the movable electrode 121 and the insulating surface ofthe substrate 100 becomes a problem when the movable electrode 121rotates. In the micro structure of the MEMS of the present invention, alowest layer of the structural layer which forms the movable portion isformed of the insulating layer (126 or the like). A layer which is incontact with a substrate surface formed of this insulating layer isformed of silicon nitride, silicon oxynitride, or silicon nitride oxide,so that friction can be reduced compared with a structural layer whichis not provided with an insulating layer.

By providing a low friction layer such that friction between the movableelectrode 121 and the substrate 100 can be reduced over the surface ofthe substrate 100, an advantageous effect of friction suppression can befurther improved. As the low friction layer, a material includingsilicon such as silicon nitride, silicon nitride oxide, siliconoxynitride, or silicon carbide, or Diamond Like Carbon (DLC) can also beused. Since DLC is minute, it has a high protective function.

Alternatively, the low friction layer can also be selectively formed inthe region in which the micro structure 11 is formed even over theentire surface of the substrate 100. The low friction layer can beformed as the insulating surface of the substrate 100 as long asinsulating properties are sufficient.

In addition, it is preferable that the low friction layer be providednot only over the surface of the substrate but also in a portion wherethe structural layers are adjacent to each other by electrostatic forceor van der Waals force. For example, when a portion in which the lowfriction layer is provided is described as for the micro structure 21 ofEmbodiment Mode 2, the inside of the opening portion 230, a connectionportion of the rotation axis 225 and the movable electrode 221, or thelike correspond to the portion in the movable electrode 221. Further, inthe micro structure 11 of Embodiment Mode 1, a portion in which themovable electrode 121 and the fixed electrode 122 are in contact witheach other also corresponds to the portion.

When the layer which forms the micro structure has a shape in whichthere is a corner seeing from a top surface, it is preferable that theshape be processed by a photolithography process and an etching processso that the corner is rounded. The sacrificial layer is similar in thisrespect. Since generation of particles can be suppressed by processinginto a round shape by removing a corner, a yield can be improved.Further, since stress concentration of the corner is relieved, a defectwhich is the cause of damage is hardly generated.

FIG. 15 is a top plan view corresponding to FIG. 1B and shows an examplein which the micro structure 11 of Embodiment Mode 1 is processed sothat a corner of the structural layer is rounded. Needless to say, eachof the micro structures of Embodiment Modes 2 to 4 can also be processedso that a corner of the structural layer is rounded.

EMBODIMENT MODE 6

A micro electro mechanical device of the present invention including amicro structure belongs to a field of micro machines and has a size of amicrometer to a millimeter. In addition, when the micro electromechanical device of the present invention is manufactured so as to beincorporated as a component of a certain mechanical device, it includesa size of a meter so that it can be easily dealt in incorporation insome cases.

A structural example of the micro electro mechanical device of thepresent invention including the micro structure is described withreference to FIG. 16. FIG. 16 is a block diagram which shows thestructural example of the micro electro mechanical device (thesemiconductor device) of the present invention. The micro electromechanical device of the present invention is not limited to only thestructural example in FIG. 16.

A micro electro mechanical device (a MEMS) 501 of the present inventionis a device in which an electric circuit portion 502 including asemiconductor element and a structural portion 503 formed of the microstructure are combined. The electric circuit portion 502 includes acontrol circuit 504 which controls the micro structure, an interface 506which communicates with an external control device 500, and the like.The structural portion 503 includes a sensor 505, an actuator 507, aswitch, or the like depending on the micro structure. An actuator is anelement which converts a signal (mainly, an electric signal) into aphysical value. An electrostatic motor like those described inEmbodiment Modes 1 and 2 can also be provided in the structural portion503.

In addition, the electric circuit portion 502 can also include a centralprocessing unit for processing data obtained by the structural portion503, or the like.

In the external control device 500, an operation such as transmitting asignal which controls the micro electro mechanical device 501, receivingdata obtained by the micro electro mechanical device 501, or supplyingdriving power to the micro electro mechanical device 501 is performed.

In addition, in the present invention, the semiconductor element whichforms such an electric circuit and the micro structure can be formedover the same insulating surface. By forming over the same insulatingsurface, a poor connection of the electric circuit or the like and themicro structure can be reduced so that the yield can be improved.

Note that in a conventional method, in the case of dealing with a minuteobject which is a millimeter or less, a process is necessary in which astructure of the minute object is enlarged so that a human or a computerreceives its data, performs data processing, and determines anoperation, and then, the operation which is reduced is transmitted tothe minute object. However, when only a broader concept instruction istransmitted by the human or the computer, the semiconductor deviceincluding the micro structure of the present invention can deal with aminute object. That is, when a purpose is determined and an instructionis transmitted by the human or the computer, the semiconductor deviceincluding the micro structure performs data processing by obtaining dataon an object using a sensor or the like so that the semiconductor devicecan take action.

In Embodiment Modes 1 to 5, it is assumed that the objects are minute.For example, it is assumed that weak signals (e.g., slight changes inlight or pressure) supplied from the objects, and the like are includedalthough the object themselves have sizes of meters.

As described above, Embodiment Modes 1 to 6 can be combined asappropriate. For example, the shape of the movable electrode 121 shownin Embodiment Mode 1 can be processed into a shape like the movableelectrode 221 shown in Embodiment Mode 2. On the contrary, the shape ofthe movable electrode 221 can be processed into a shape like the movableelectrode 121.

EMBODIMENT 1

In this embodiment, an example is described in which structural layersare formed of semiconductor layers having different crystallinestructures as described in Embodiment Mode 2 and the like.

As described n Embodiment Mode 2 and the like, for example, siliconlayers having different crystalline structures like a polycrystallinesilicon layer and an amorphous silicon layer have different mechanicalcharacteristics. Therefore, by stacking the silicon layers, a microstructure which is appropriate for various uses can be manufactured.

<Measurement of complex elastic modulus and indentation hardness>

In order to examine difference in mechanical characteristics of siliconlayers having different crystalline structures, measurement of complexelastic moduli and indentation hardness of an amorphous silicon layerformed by CVD and a crystalline silicon layer obtained by crystallizingamorphous silicon was performed. Here, the crystalline silicon layer wasobtained by laser crystallizing an amorphous silicon layer using a metalelement.

The amorphous silicon layer used as a sample was formed as follows.First, a silicon nitride layer having a thickness of 50 nm and a siliconoxide layer having a thickness of 100 nm were formed over a quartzsubstrate as base layers by CVD. Then, an amorphous silicon layer havinga thickness of 66 nm was formed over the base layers by plasma CVD.

In addition, the crystalline silicon layer used as a sample was preparedas follows. An amorphous silicon layer having a thickness of 66 nm wasformed by plasma CVD. Nickel was added to the amorphous silicon layerand the amorphous silicon layer was crystallized by using a continuouswave laser. Thickness of the crystalline silicon layer crystallized bylaser irradiation was approximately 60 nm. A laser beam used forcrystallization was a second harmonic wave of an Nd:YVO₄ laser; energydensity of the laser was controlled in a range of greater than or equalto 9 W/cm² and less than or equal to 9.5 W/cm²; and scan speed was setto 35 cm/sec.

Measurement was performed by nano indentation measurement in which atriangular pyramid-shaped indenter was pushed into the sample. Ameasurement condition was simple indentation and an indenter which wasused was a Berkovich indenter made of diamond. Therefore, an elasticmodulus of the indenter was approximately 1000 GPa and a Poisson's ratiothereof was approximately 0.1.

A complex elastic modulus which was measured was represented by thefollowing Formula 1 and was an elastic modulus in which an elasticmodulus of the sample and the elastic modulus of the indenter weremixed. In Formula 1, Er corresponds to a complex elastic modulus; Ecorresponds to a Young's modulus; and ν corresponds to a Poisson'sratio. In addition, a first term of the formula (a term shown by“sample”) is a term to which the elastic modulus of the samplecontributes and a second term of the formula (a term shown by“indenter”) is a term to which the elastic modulus of the indentercontributes.

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{\mspace{85mu}{\frac{1}{Er} = {\left( \frac{1 - v^{2}}{E} \right)_{sample} + \left( \frac{1 - v^{2}}{E} \right)_{indenter}}}} & (1)\end{matrix}$

As shown in Formula 1, the complex elastic modulus can be calculatedfrom the sum of the first term to which the elastic modulus of thesample contributed and the second term to which the elastic modulus ofthe indenter contributed. However, since the elastic modulus of theindenter was extremely higher than that of the sample, the second termcan be ignored and the complex elastic modulus approximately shown theelastic modulus of the sample.

Further, indentation hardness was hardness measured by an indentationmethod and can be calculated by dividing the maximum indentationweighting by a projection area in maximum indentation. Here, aprojection area in indentation can be calculated by a geometric shape ofthe indenter and a contact depth when the sample was pushed by theindenter. This indentation hardness was multiplied by 76, so thatindentation hardness can be dealt equally to Vickers hardness which wasgenerally used as an index of hardness.

Measurement results of the complex elastic moduli and indentationhardness of the crystalline silicon layer and the amorphous siliconlayer are shown in Table 1. Numeric values in Table 1 are an averagevalue of three-times measurement results.

From the results shown in Table 1, crystalline silicon had a higherelastic modulus than that of amorphous silicon. That is, the resultsshowed that crystalline silicon had higher strength for damage bybending than amorphous silicon when force bending a structure wasapplied. Further, the results showed that crystalline silicon was harderthan amorphous silicon.

TABLE 1 Complex elastic Indentation Sample modulus (GPa) hardness (GPa)Amorphous silicon 141 15.5 Crystalline silicon 153 20.3

By stacking the semiconductor layers having different complex elasticmoduli and hardness in this manner, structural layers having both strongflexibility and hardness toward bending force can be manufactured. Forexample, by stacking the amorphous silicon layer and the crystallinesilicon layer used as the sample in this embodiment, damage was hardlyspread over amorphous silicon even when damage was generated from acrystal defect of crystalline silicon, so that damage can be preventedfrom being caused to amorphous silicon. In this manner, balance betweenflexibility and hardness of the structural layers can be determineddepending on a thickness ratio of stacked layers.

This application is based on Japanese Patent Application serial No.2006-196403 filed in Japan Patent Office on Jul. 19, 2006, the entirecontents of which are hereby incorporated by reference.

1. A manufacturing method of a micro electro mechanical devicecomprising a micro structure and an electric circuit formed over asubstrate having an insulating surface, comprising the steps of: forminga first conductive film over the substrate; processing the firstconductive film to form a first sacrificial layer in a first region anda gate electrode of a transistor in a second region; forming a firstinsulating layer and a first semiconductor layer over the substrate, thefirst sacrificial layer and the gate electrode; forming a secondsemiconductor layer over the first semiconductor layer; processing thefirst insulating layer, the first semiconductor layer and the secondsemiconductor layer to form a first structural layer and a secondstructural layer in the first region and a gate insulating film and asemiconductor layer of the transistor in the second region; forming asecond conductive film over the substrate, the first structural layer,the second structural layer and the semiconductor layer of thetransistor; processing the second conductive film and a portion of thesemiconductor layer of the transistor to form a second sacrificial layerin the first region and to form a channel formation region, a sourceregion, a drain region and electrodes which are electrically connectedto the source region and the drain region in the second region; forminga second insulating layer over the substrate, the channel formationregion, the second sacrificial layer and the electrodes; removingpartially at least a portion of the second insulating layer in the firstregion; forming an opening which penetrates the first sacrificial layerand the second sacrificial layer; forming a rotation axis in theopening; and removing the first sacrificial layer and the secondsacrificial layer, so that the micro structure including the firststructural layer movable with respect to the substrate and the secondstructural layer which is partially fixed to the substrate is formed. 2.A method for manufacturing the micro electro mechanical device accordingto claim 1, wherein the second conductive film includes a metal elementand a compound of a semiconductor and the metal element is formed byreacting the second conductive film and the semiconductor layer of thefirst region.
 3. A method for manufacturing the micro electro mechanicaldevice according to claim 1, wherein the micro structure includes arotor formed of the first structural layer.
 4. A manufacturing method ofa micro electro mechanical device comprising a micro structure and anelectric circuit formed over a substrate having an insulating surface,comprising the steps of: forming a first conductive film over thesubstrate; processing the first conductive film to form a firstsacrificial layer in a first region and a gate electrode of a transistorin a second region; forming a first insulating layer and a firstsemiconductor layer over the substrate, the first sacrificial layer andthe gate electrode; forming a second semiconductor layer over the firstsemiconductor layer; processing the first insulating layer, the firstsemiconductor layer and the second semiconductor layer to form a firststructural layer and a second structural layer in the first region and agate insulating film and a semiconductor layer of the transistor in thesecond region; forming a second conductive film over the substrate, thefirst structural layer, the second structural layer and thesemiconductor layer of the transistor; processing the second conductivefilm and a portion of the semiconductor layer of the transistor to forma second sacrificial layer in the first region and to form a channelformation region, a source region, a drain region and electrodes whichare electrically connected to the source region and the drain region inthe second region; forming a second insulating layer over the substrate,the channel formation region, the second sacrificial layer and theelectrodes forming a contact hole in the second insulating layer;forming a third conductive film over the second insulating layer;processing the third conductive film to form wirings being in contactwith the electrodes; removing partially at least a portion of the secondinsulating layer in the first region; forming an opening whichpenetrates the first sacrificial layer and the second sacrificial layer;forming a rotation axis in the opening; and removing the firstsacrificial layer and the second sacrificial layer, so that the microstructure including the first structural layer movable with respect tothe substrate and the second structural layer which is partially fixedto the substrate is formed.
 5. A method for manufacturing the microelectro mechanical device according to claim 4, wherein the secondconductive film includes a metal element and a compound of asemiconductor and the metal element is formed by reacting the secondconductive film and the semiconductor layer of the first region.
 6. Amethod for manufacturing the micro electro mechanical device accordingto claim 4, wherein the micro structure includes a rotor formed of thefirst structural layer.